Prof. Carus on the relative Proportions of the Eye. 41 

 Crustacea and MoUusca are invested with a dense vegetable co- 



On the relative Proportions of cei'tain parts of the Eye of tlie 

 Foetus^ compared with the same parts of the perfectly de- 

 veloped Eye. By Professor Carus. 



JL HE remark has ah'eady been made by some anatomists and 

 physiologists, that the human eye, as well as all the organs, runs 

 through a series of degrees of development, in which its analogy 

 with the eye of animals is so much the greater, the nearer it is 

 to its first formation. The object of Professor Carus, in his 

 memoir, is to follow out this proposition in some of its details. 

 The following are among the most interesting results of his in- 

 vestigation. 



The eye of man, compared with that of animals, presents -the 

 most extended retina, in proportion to the size of the. eye-ball 

 (consult Sommering''s Plates, De Oculorum hominis ariimor- 

 Uumque sectione hj)rizontaVi, Gotting. 1818). The vitreous 

 body of the human eye 'Hi the largest of all, compared with 

 the bulk of the crystalline humour : the portion of the eye-ball 

 which covers the transparent cornea, and which allows the iris 

 and pupil to appear, is smaller in proportion to the part which 

 the sclerotic covers ; and this proportion is modified only in 

 birds, especially the birds of prey, in which the extraordinary 

 breadth of the ciliary processes puts limits to the extension of 

 the retina, which is kept at a distance from the edge of the cor- 

 nea. In the eye of animals, also, the sclerotic scarcely appears 

 imder the palpebrae, while a considerable portion of it is visible 

 in the human eye. 



It is equally observed, in the different forms of the latter, 

 that the relation of the extent of the iris and pupil, to the sur- 

 face of the visible portion of the sclerotic, is not always the same. 

 In children, the iris and pupil have a greater proportional ex- 

 tent, exhibiting an analogy with the eye of animals ; and in 

 adults a large iris with its pupil, seems to us rather to be the 

 expression of physical power, while an eye in which the contrary 

 takes place, and in which the sclerotic coat shews itself to a great 



